    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *     http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.configuration2.interpol;
    018
    019
    020/**
    021 * <p>
    022 * A specialized lookup implementation that allows access to environment
    023 * variables.
    024 * </p>
    025 * <p>
    026 * This implementation relies on {@link System#getenv()} to resolve
    027 * environment variables. It can be used for referencing environment variables
    028 * in configuration files in an easy way, for instance:
    029 * </p>
    030 *
    031 * <pre>
    032 * java.home = ${env:JAVA_HOME}
    033 * </pre>
    034 *
    035 * <p>
    036 * {@code EnvironmentLookup} is one of the standard lookups that is
    037 * registered per default for each configuration.
    038 * </p>
    039 *
    040 * @author <a
    041 *         href="http://commons.apache.org/configuration/team-list.html">Commons
    042 *         Configuration team</a>
    043 * @since 1.7
    044 * @version $Id: EnvironmentLookup.java 1843310 2018-10-09 16:43:53Z ggregory $
    045 * @deprecated Use {@link DefaultLookups#ENVIRONMENT}.
    046 */
    047@Deprecated
    048public class EnvironmentLookup implements Lookup
    049{
    050    /**
    051     * Performs a lookup for the specified variable. This implementation
    052     * directly delegates to a {@code System.getenv()}.
    053     *
    054     * @param key the key to lookup
    055     * @return the value of this key or <b>null</b> if it cannot be resolved
    056     */
    057    @Override
    058    public String lookup(final String key)
    059    {
    060        return System.getenv(key);
    061    }
    062}